What are the earliest sources that refer to Jewish mysticism in particular as "kabblah".

(Preferably the answer should include an indication that the word was associated with this in particular, rather than just being used for mysticism as an example of things which are received by tradition).

(my attempt at a translation) And similarly the great Name which I mentioned (the 72-letter name) is entirely contiguous, and it can be divided into groups of three letter words, in many permutations, as its usage is knows to the masters of the kabbalah.